Two adventurous young boys come across a scruffy vagrant living in a boat in a tree, and become involved in a plot involving murder, obsession and revenge.

But this is mainly a story about love.

“Mud,” a film-fest favorite now going mainstream with a strong cast mixing recognizable stars with fresh faces, is a terrific story oozing Southern pulp and personality, shot on location in Arkansas.

Tye Sheridan, who played one of the young sons in “The Tree of Life” (2011), is Ellis, a 14-year-old river rat who along with his buddy Neckbone (Jacob Lofland) comes upon an amazing find: a flood-stranded wooden boat on an uninhabited island in the middle of the Mississippi River.

Just as they claim it as their own, they’re surprised to meet the squatter who’s already made it his home. Mud (Matthew McConaughey) has a pack a cigarettes, a pistol tucked into his pants, boots with crosses in their heels, and wild stories about Mexicans, Indians, wolf’s eyes and snakes—and a price on his head for the murder of a man who was abusing the only woman he’s ever loved.

That woman, a honky-tonk angel named Juniper (Reese Witherspoon), is supposedly coming to reunite with Mud on the island. Ellis and Neckbone agree to help Mud get his boat, and his plan, afloat before the family of the man he killed can get to him.

“Mud” feels like a movie adapted from a book or a great American short story, but it was actually based on the original screenplay written by its Arkansas-born director, Jeff Nichols, and it marks only his third movie, following his other highly praised film-festival hits, “Shotgun Stories” and “Take Shelter.” Judging from these three movies, Nichols looks to be well on his way to becoming a major talent.

For all its sweaty, swamp-adventure overtones, “Mud” is actually a tale of bruised romance filtered through several fractured prisms. The word “love” probably comes up at least two dozen times, especially as Ellis tries to sort out the confusing signals he gets about what it is, how it feels, and how people supposedly in it treat each other.

Ellis’ bickering parents (Sarah Paulson and Ray McKinnon, two fine character actors with more than 120 credits between them) are going through a divorce; Neckbone, whose mother and father are both out of the picture, lives with his promiscuous uncle Galen (Michael Shannon; too bad there’s not much more of him here); Mud and his childhood crush, Juniper, could be subjects in a textbook on toxic co-dependence.

Jo Don Baker is the patriarch of the death squad hell-bent on finding Mud, and Sam Shepherd plays Ellis’ broody across-the-river neighbor, a widower whose past father- figure relationship with Mud is a matter of mystery, if not larger significance.

And all this is woven around Ellis’ attempts to woo a crush of his own, an older girl (Bonnie Sturdivant) who’s initially impressed with the hot-tempered stand he makes for her honor.

Ellis doesn’t have one example anywhere of a positive role model. Like Neckbone’s uncle Galen, using a homemade lighted diving helmet to grope through the murky clouds of silt as he works the river for his livelihood of mussels, everyone in “Mud” has trouble seeing anything clearly as they stumble around in their own sludge when it comes to matters of the heart.

This nugget of a film, a modern-day Huck Finn adventure pulled along in the mesmerizing current of a crime yarn and anchored to a teenager’s heartbreaking quest for emotional moorings, is definitely worth plucking from the river of summer movies. “Mud” is a keeper.